在化学教学过程中，往往对某种物质是否形成或存在，要求作出迅速判断，用纸上斑点反应可以解决这类难题。其原理是：当待试溶液与试剂溶液在滤纸上互相渗合在一起时，其显色反应的产物就固定于滤纸表面，且在被水润湿的圆圈内局部聚集成斑点或环圈。这样，就能迅速准确地判断 In the chemistry teaching process, it is often required to make a quick judgment as to whether or not a certain substance is formed or existed, and a paper spot reaction can solve such problems. The principle is that when the solution to be tested and the reagent solution are infiltrated with each other on the filter paper, the product of the color reaction is fixed on the surface of the filter paper, and spots or loops are locally gathered in the water-wetted circle. In this way, you can quickly and accurately determine